The present invention relates to ink suitable for ink-jet recording, and an ink cartridge and a recording apparatus including such ink.
Conventionally, as the ink used for ink-jet recording, ink containing a coloring material (e.g. dye and pigment), a humectant, a penetrant, and water is well known. The humectant is contained for preventing drying of the ink in an ink-jet head. The penetrant is contained for improving the penetration of the ink into recording paper.
As the dye, water-soluble dye is often used. However, to enhance, for example, water resistance on recording paper, oil soluble dye is preferably used. As ink using an oil soluble dye, known is ink essentially composed of an oil soluble dye, polyoxyethylene oxypropylenetriol, and an aqueous acrylic resin solution or a water-soluble acrylic resin emulsion (see Japanese Laid-Open Patent Publication No. 10-140055). Also known is ink composed of a colored emulsion where a polymer obtained from a dye composition of a monomer composition blended with an oil soluble dye is dispersed in a water-type medium (see Japanese Laid-Open Patent Publication No. 2000-154341).
There is also proposed a technique for dissolving an intrinsically water-insoluble oil soluble dye in water using, as an additive, an amphiphilic star block polymer or an amphiphilic heteroarm star polymer (Polymer Preprints, Japan Vol. 49, No. 1 (2000) pp. 22–24, Macromolecules, Vol. 24, No. 21 (1991) pp. 5741–5745, Macromolecules, Vol. 25, No. 24 (1992) pp. 6407–6413).
Ink used for ink-jet recording must be low in viscosity to some extent. If the viscosity is too high, the ink fails to fly from a nozzle of an ink-jet head as a liquid drop. The ink also must be sufficiently stable so as to be free from coagulating in an ink tank or clogging a nozzle and the like. However, none of the conventional ink containing a coloring material insoluble in water such as oil soluble dye is adequate as the ink for ink-jet recording from the standpoints of viscosity and stability.
For example, the ink disclosed in Japanese Laid-Open Patent Publication No. 10-140055 has a viscosity of about 10000 mPa·s, which is too high for use for ink-jet recording. The ink disclosed in Japanese Laid-Open Patent Publication No. 2000-154341 can have a reduced viscosity, but is poor in stability because it is difficult to maintain the dispersion state for a long time. This ink therefore tends to coagulate during storage or clog an ink head.
A solution obtained from the technique described in Polymer Preprints, Japan Vol. 49, No. 1 (2000) pp. 22–24 is high in surface tension and thus low in the speed of penetration into paper. Therefore, when this ink is used for ink-jet recording, a jetted ink drop dries less easily, causing considerable smearing of characters and images formed on the paper with the ink drop. In addition, since the solution is slow in drying, the oil soluble dye is hard to stay on the surface of the paper. The oil soluble dye rather tends to penetrate through the paper to reach the back of the paper, causing so-called strike-through. Duplex printing is therefore difficult.
In view of the above, ink containing an oil soluble dye and yet having low viscosity and high stability has been desired. The object of the present invention is to provide ink for ink-jet recording that exhibits excellent water resistance on ordinary paper, has high stability, smears less easily, enables duplex printing, and provides recorded products with high printing quality and high image quality, and an ink cartridge and a recording apparatus including such ink.